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UIC option in SPICE?

Discussion in 'Electronic Basics' started by billcalley, Jun 23, 2005.

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  1. billcalley

    billcalley Guest

    I have read all I could find about the Use Initial Conditions (UIC)
    option in SPICE, but I still don't fully understand it. The reason I
    am confused is this: When I run a DC transient analysis with UIC
    enabled on a simple RLC tank circuit (with all passives having an IC of
    '0'), shouldn't these results be the same as a DC transient
    simulation with *no* UIC, since they should both have a initial
    starting condition of 0V/0A? Yet with the simulation with no UIC
    enabled, the circuit reaches steady state instantly; while with the UIC
    option enabled it takes a finite time to reach its voltage level, then
    over/undershoots a few time (rings) -- as it should. What am I missing

    Thank You,

  2. If UIC is not specified then SPICE does not assume zero initial conditions.
    By default SPICE will solve for the DC operating point of the circuit before
    performing a transient analysis, and use that for the initial conditions.

    The originating message was also posted to sci.electronics.cad but was not
    cross-posted, so I have cross-posted now.

  3. billcalley

    billcalley Guest

    Thanks very much for the clear answer Jonathan! Very much appreciated.

    Best Regards,

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